Collision and Fade Localization within Packets for Wireless LANs

Abstract

In this paper, we derive an algorithm for estimating the location of events which cause burst errors, such as packet collisions and multipath fades in wireless packets. Effective localization algorithms have a range of applications, and could lead to network performance improvements through techniques such as error control coding and cross-layer design between the physical and medium access control layers. Given that a collision or fade occurs in a packet, the algorithm finds the maximum-likelihood estimate of the start time and duration of the collision or fade. Due to the computational complexity of this optimal estimate, we also derive an efficient sub-optimal algorithm which decouples the estimation of the collision or fade duration from the estimation of its starting position within the packet of interest. Both algorithms are able to isolate collision locations within the packet when the signal-to-noise ratio is high enough for the link to operate at a BER of ~10?6 in the absence of collision. An extension to M-QAM demonstrates similar effectiveness for constellation sizes up to 128.